(a) Field of the Invention
The invention relates to a communication device, particularly to a communication device that is capable of eliminating near-end cross talk and dynamically adjusting the high-frequency response.
(b) Description of the Related Art
FIG. 1 shows a schematic diagram illustrating a communication device in the prior art. The communication device 10 comprises a transmitting medium 11, a hybrid circuit 12, a local transmitting circuit Tx, and a local receiving circuit Rx. The communication device 10 can perform signal transmission and reception with a far-end communication device via the transmitting medium 11. Generally, the local transmitting circuit Tx comprises a digital to analog (DA) converter (not shown) for converting a signal into an analog signal to generate a transmission signal STX that is then outputted through the hybrid circuit 12 and the transmitting medium 11. The local receiving circuit Rx comprises an analog to digital (AD) converter for performing analog to digital conversion on the receiving signal SRX inputted via the hybrid circuit 12 and the transmitting medium 11.
Since signal transmission and reception of the communication device 10 usually occur at the same time, while the local receiving circuit Rx of the communication device 10 receives the signal SRX from the far-end communication device, the local receiving circuit Rx is interfered by the echo bounced back from the far-end communication device after the local transmitting circuit Tx of the communication device 10 transmits a signal and also interfered by near-end cross talk (NEXT) to result in lowering communication quality of the communication system.
Furthermore, the power of the signal SRX received by the local receiving circuit Rx of the communication device 10 is reduced due to transmission distance and the local receiving circuit 13 also simultaneously receives echo and crosstalk signals (high-frequency noise), the power of which is much larger than the signal SRX.
In order to correspondingly process the effect generated by the partial response filter (not shown) in the far-end transmitting circuit, generally the local receiving circuit Rx is provided with a high pass filter (HPF) (not shown) for having the high frequency component pass, such as inverse partial response filter (IPR) (not shown). Since there are many near-end interferences and the signal passing through the inverse partial response filter has its high-frequency component boosted or increased, the signal peak-to-average ratio of the near-end interference (such as echo and crosstalk interferences) is increased and relatively the signal peak-to-average ratio of the whole including the far end and the near end is also increased, that is, the peak value of the signal is increased.
In order to completely receive and process the signal having an increased peak value, the dynamic range of the analog to digital (AD) converter of the local receiving circuit Rx should be designed to be large. Thus, the design of the communication device becomes complicate to result in increasing production cost. But, reducing the cost of the analog to digital (AD) converter will result in limiting the effect of the inverse partial response filter.